Known feedthroughs and sealing bodies of this kind function to provide a fire-protecting seal whereby a path for the conductor, separated into fire-resistant segments by the wall, are sealed with respect to one another in a fire-resistant manner. In addition to maxium fire retardation, the feedthroughs and the sealing bodies should have the best possible sealing properties against water, gas and smoke. The known sealing bodies are made of synthetic rubber, such as neoprene or chloroprene, to which, for the desired fire-resistance duration, fire retardant and expanding materials and the like are added. The admixture of these substances to the rubber composition, however, reduces considerably the technical value of the rubber mixture. For example, hardening occurs in the rubber with the addition of relatively small quantities of additives. When the quantity of the additives corresponds to the desired duration of fire-retardant properties, the rubber body can be hardened so much that it may have insufficient elasticity and cannot provide a satisfactory seal against water, gas or smoke. It is also necessary to provide an elastic rubber which is as soft as possible so that the sealing body will adhere snugly to the conductor and the wall of the opening when pressed into the opening. Besides, these rubber mixtures with such additives are expensive, since the admixing process is quite involved. This, in turn, leads to the high cost of such special rubber mixtures. Finally, such sealing bodies, which usually are dimensioned to be quite thick, require extended vulcanization times, so that the forms in which the sealing bodies are vulcanized remain occupied for long times, thereby also contributing to production costs.